When transporting a fluid containing both gas and liquid over longer distances such as when transporting unprocessed or partly processed well fluid from an off-shore production system to an on-shore processing facility, or when transporting unprocessed or partly processed well fluid from on off-shore production system to a platform processing facility, transient liquid flow or liquid slugs partly containing hydrocarbons (condensate and oil) and/or water tend to be created in the pipeline either due to seabed terrain effects, and/or transient operation of the pipeline. The liquid in the fluid flow of the pipeline will, depending on the velocity of the fluid, tend to accumulate in the pipeline. At high velocities the liquid will continuously be transported together with the gas. On the other hand, with lower velocities the liquid will accumulate at the uphill parts of the pipeline as mentioned above. As the velocities are increased the accumulated liquid will be disposed from the pipeline into the downstream facilities either as liquid slugs or liquid surges. Such liquid slugs or surges may exceed the liquid handling capacity of the downstream processing facilities and cause operational problems, and may, at high velocities, cause sever damage to the process equipment being connected to the downstream end of the pipeline.
Different types of slug catchers are previously known which are designed to deal with slugs in multiphase flow pipelines. One type which is commonly used is the so-called finger-type slug catcher consisting of multiple parallel pipes being connected to a common unit and which is capable receiving and buffer an arriving slug. Such known slug catcher is, however, very heavy, large and space consuming and therefore represent a very expensive solution when used on onshore or at off-shore platforms as the platforms must be specially designed for such heavy and spacey piece of equipment.
WO 03/067146 A1 relates to a sub sea multiphase pipeline with integrated slug-catcher where the sub sea pipeline comprises at least one section with a tendency to the formation of slugs at a multiphase flow in an upward slope, and where at a low point in said section is provided at least one downwards directed branch being connected to a second pipeline to enable separation of liquid from such lower point in the sub sea pipeline to the second pipeline.
One major disadvantage with this known solution is that it will not enable sufficiently speedy separation of fluid of slugs containing large amounts of liquid, whereby the slugs will pass by, and proceed further downstream of the separation point.